What was found
AFTER TAKEOFF FROM TOL, NR 4 ENGINE EXPERIENCED A COMPRESSOR STALL, THE FLIGHT RETURNED TO TOL. MAINTENANCE TROUBLESHOT THE EPR SYSTEM, INTERSTAGE BLEED VALVE, AND CLEANED THE PS4 FILTER. OPERATIONAL CHECKS OF THE ENGINE, INDICATION SYSTEMS AND BLEED VALVE WERE ACCOMPLISHED WITH NO FAULTS FOUND. THE AIRCRAFT WAS RETURNED SERVICE. (M)